Audio signals provided through a broadcasting service such as television (TV) broadcast, radio broadcast, and digital multimedia broadcast are acquired by combining audio signals of diverse sound sources into audio signals of a form, and storing and transmitting the audio signals of a form.
In this environment, viewers can adjust the signal strength of the entire audio signals but they cannot control the characteristics of audio signals of each sound source, for example, they cannot control signal strength of audio signals of a specific sound source included in the audio signals of the combined form.
However, if an audio content is authored not by combining audio signals of respective sound sources but by storing them independently, a content reproduction terminal can provide the audio content to the viewers with an option of controlling signal strength of audio signals of each sound source. An audio service for independently storing/transmitting a plurality of audio signals in a storing and transmitting block so that viewers could watch controlling each audio signals properly in a receiver, which is the content reproduction terminal, is called ‘an object-based audio service.’
Differently from typical MP3, Advanced Audio Coding (AAC), the object-based audio content includes several audio objects. Moving Picture Experts Group (MPEG) 4 system specification (ISO/IEC 14496-1), which defines a file structure of a content including several objects, may be applied for storing object-based audio contents.
Typically, most multimedia services are formed of one audio object and one video object. MPEG-4 system specification, however, defines a multimedia service including a plurality of objects. The object-based audio service, too, can be called a multimedia contents service including a plurality of objects, which is similar to what is defined in the MPEG-4 system specification.
However, while the MPEG-4 system specification defines a file structure including diverse kinds of media such as audio, video, still picture and the like, an object-based audio content includes objects of the same kind. Thus, the object-based audio service can store contents more efficiently than the file structure defined in the MPEG-4 system specification and ease access to each object.
Meanwhile, the MPEG-4 system specification (ISO/IEC 14496-1) also defines a file structure of a content including a plurality of objects. The file format of the MPEG-4 system specification includes ‘BIFS’, ‘OD’, and ‘index information.’ ‘BIFS’ is three-dimensional (3D) scene information of objects and ‘OD’ is information on objects. ‘Index information.’ is information for accessing to stream of each object, which will be referred as object stream. Data of each object may be inside a file or they may be formed as another file. The ‘index information’ for object stream is formed and stored separately for each object, and object streams are also divided and stored for each stream.
In the respect of easy access to an object, the conventional object-based audio content service according to the MPEG-4 system specification has a problem of remarkably low access property to an object, when a plurality of objects are stored. This is because the conventional object-based audio content service stores frames for each for object or data of the entire objects sequentially.
Also, the conventional object-based audio content service uses position information and size information of each frame as the ‘index information’ to make random access to objects of a content file even easier. However, the conventional index information creating method creates index information based on the least reproduction unit of each medium, which is a frame in case of audio. In other words, index information should be created on a frame basis. Therefore, a great deal of index information is generated and the amount of operations for acquiring index information is also huge. Thus, it takes long time to make a random access.
Meanwhile, the MPEG-4 system specification can change three-dimensional (3D) scene information through user interaction by using BIFS data and BIFS commands. In an authoring step, BIFS data are properly created based on the changed 3D scene information. A content reproduction terminal should be able to analyze BIFS commands. As described above, the MPEG-4 system specification includes diverse functions for user interaction. To have such functions, the authoring step or the content reproduction terminal requires a little complicated operation.
However, if a user controls the position and sound volume of each audio object in the object-based audio service, new 3D audio scene information (which is preset) can be created easily.
If a user can freely create audio preset or add/delete/change an object of an object-based audio content file, the functions of the object-based audio service can be enhanced through user interaction.
Therefore, it is required to develop an efficient content file structure that can enhance functions of the object-based audio service and make access to each object easier in an object-based audio content service.